Auto merge of rust-lang#131422 - GnomedDev:smallvec-predicate-obligations, r=compiler-errors

Use `ThinVec` for PredicateObligation storage

~~I noticed while profiling clippy on a project that a large amount of time is being spent allocating `Vec`s for `PredicateObligation`, and the `Vec`s are often quite small. This is an attempt to optimise this by using SmallVec to avoid heap allocations for these common small Vecs.~~

This PR turns all the `Vec<PredicateObligation>` into a single type alias while avoiding referring to `Vec` around it, then swaps the type over to `ThinVec<PredicateObligation>` and fixes the fallout. This also contains an implementation of `ThinVec::extract_if`, copied from `Vec::extract_if` and currently being upstreamed to Gankra/thin-vec#66.

This leads to a small (0.2-0.7%) performance gain in the latest perf run.

Author: bors

Cargo.lock

@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "addr2line"
@@ -3857,6 +3857,7 @@ dependencies = [
  "rustc_target",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4496,6 +4497,7 @@ dependencies = [
  "rustc_transmute",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4567,6 +4569,7 @@ dependencies = [
  "rustc_span",
  "rustc_type_ir_macros",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -18,6 +18,7 @@ use rustc_infer::infer::region_constraints::RegionConstraintData;
 use rustc_infer::infer::{
     BoundRegion, BoundRegionConversionTime, InferCtxt, NllRegionVariableOrigin,
 };
+use rustc_infer::traits::PredicateObligations;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -40,7 +41,6 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::sym;
 use rustc_span::{DUMMY_SP, Span};
 use rustc_target::abi::{FIRST_VARIANT, FieldIdx};
-use rustc_trait_selection::traits::PredicateObligation;
 use rustc_trait_selection::traits::query::type_op::custom::{
     CustomTypeOp, scrape_region_constraints,
 };
@@ -2940,7 +2940,7 @@ impl NormalizeLocation for Location {
 pub(super) struct InstantiateOpaqueType<'tcx> {
     pub base_universe: Option<ty::UniverseIndex>,
     pub region_constraints: Option<RegionConstraintData<'tcx>>,
-    pub obligations: Vec<PredicateObligation<'tcx>>,
+    pub obligations: PredicateObligations<'tcx>,
 }
 
 impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {